[R] newbie question

[Larry White]

Sorry - this must be obvious, but i haven't been able to find the
answer in the guides i've searched.  The examples seem to assume you
always want to look at all the data.

I want to be able to filter data in a dataframe before analyzing it.
For example, I'd like to plot(a,b) but only include values where b >
1000.

I'd also like to be able to do similar filtering before doing other
statistical functions.

Thanks for your help.